The National Audit Office has produced a report criticising parts of the project.

It is the latest in a long line of controversies surrounding the 10-year programme.

What is happening?

The programme is being run by a government agency called NHS Connecting for Health.

By 2014, 30,000 GPs in England will be linked up to nearly 300 hospitals giving the NHS a "21st century" computer network.

It involves an online booking system, Choose and Book, a centralised medical records system for 50m patients, e-prescriptions and fast computer network links between NHS organisations.

It is said to be the most ambitious computer project in the world and represents the largest single investment in IT in the UK.

Why is it being done?

Most agree the NHS has never spent enough on IT, so it is understandable the system is being upgraded.

But it also has to be seen in the context of government reforms. From the beginning of this year, patients have been able to choose from different hospitals for non-emergency operations.

This is expected to be expanded out to other parts of health care in forthcoming years.

To make this achievable, it is clear a fully integrated IT system is a necessity.

How much is it costing?

The system is set to cost £6.8bn extra over 10 years.

In addition, when the training and local implementation is taken into account, the figure rises to over £12bn.

The government has also said if you include spending on the current IT systems while the new network is introduced the figure will rise to about £20bn.

Why has it been controversial?

Despite the government's enthusiasm, the system has not proved popular with doctors and IT professionals.

Doctors have consistently complained they were not fully consulted about the system.

They have also expressed concerns about patient confidentiality as the electronic records system allows health professionals anywhere in the country to access highly sensitive data.

Leading IT experts wrote to MPs in April questioning whether the programme had been properly designed to meet the needs of 24-hour health care.

They pointed out the nature of the NHS means it would have to support huge volumes of data and traffic.

Key parts of it are also falling behind schedule. The Choose and Book system is now not due to be fully implemented until next year - 12 months after planned.

Meanwhile, the electronic records system is delayed by more than two years.

Why have things gone wrong?

Any IT project to link up the NHS all up was always going to face tough challenges and high cost.

Tony Collins, of Computer Weekly magazine said the job of introducing an NHS-wide IT system was simply bigger than the government expected.

"The NHS comprises hundreds of businesses, and it was more complicated, more time-consuming and more expensive than they thought."

What is the National Audit Office saying?

The watchdog has warned that the project faces significant challenges if it is going to be successfully implemented.

Key parts of the project, such as the online booking system, Choose and Book, and the electronic care records, are behind schedule.

The report is also critical about the lack of engagement with clinicians.

But the watchdog said the costs of delays will not be passed on to tax payers as the contracts agreed with suppliers have tight restrictions in place putting the onus on them to deliver on time or pay the price.

The NAO also found the project was running more or less to budget - although the cost of the contracts had increased slightly from £6.2bn to £6.8bn because different aspects have been added.

However, the report added it was too early to tell if they project represented value for money.